Hello my problem is when I click preheat to PLA and printer heat up to the right temperature, temperature is constant and stable but when I start printing immmdiately temperature jumps up and down and is not constant. I buy new thermistor and replace but this not fix my problem so I decide to post this because I don't have any other idea to solve this problem. Do you have any ideas to help me?Link to video show the problem: https://streamable.com/ff2ttw